The campaign to approve potential upgrades at the Crandon Park Tennis Center has drawn opposition from a member of the pioneering family that donated the park land to the county.

Bruce Matheson, who sits on a four-member committee that governs future plans for the park, called for a “resounding NO” vote on the Miami-Dade ballot measure in a full-page color ad in Sunday’s Miami Herald.

“The ballot language is incomplete, which prevents any voter from making an informed decision,” Matheson said in an interview.

Not so, counter Sony Open tennis tournament organizers pushing for the ballot measure, which has drawn the support of Miami-Dade Mayor Carlos Gimenez and conditional support from the Key Biscayne Village Council.

The proposed charter amendment would allow tournament organizers to seek commission approval for a nearly $50-million makeover, paid for by the tournament and tournament revenues, such as parking surcharges and ticket fees. In his ad, Matheson called the plans a “50-year sweetheart contract” for the tournament, whose lease — set to expire in nine years — would be extended to a total of 30 years, with two optional, 10-year extensions.

Financing the project would most likely require Miami-Dade County to issue revenue bonds backed by the tournament. County commissioners only agreed to put the measure on the ballot under the condition that the tennis center upgrades would not be paid for from the county’s general fund.

Matheson questioned whether the county would be on the hook to pay back any debt taken on for the project if the tournament were to go out of business or leave town.

“What he’s trying to do is confuse the issue,” said Gene Stearns, the tournament’s attorney, who called it “absolutely, totally, completely untrue” that the county would have to step in to pay back the bonds.

The bonds would be backed solely by tournament revenues. Were those revenues to dry up, the bondholders would be left holding the bag. The county’s credit rating would not likely take a hit and it would not be on the hook, said Broward County Commissioner John Rodstrom, who works in the bond industry and is not affiliated with the ballot measure’s proponents.

“The bondholders are not buying those bonds looking to be bailed out by the county,” he said.

Tournament organizers created a political committee to campaign for the ballot measure. The Committee to Preserve an Ideal Partnership has mailed campaign fliers, put up signs and aired Spanish-language radio ads featuring retired tennis players Mary Joe Fernandez and Fernando Gonzalez.

The tournament has proposed building permanent grandstands, shaded pavilions and multi-story additions to the tennis center’s stadium. The improvements are necessary, they say, to keep the popular Sony Open — known as professional tennis’ “fifth Grand Slam” — in Key Biscayne. Rival tournaments have upgraded their facilities to attract big-name players.

The proposal requires approval from two-thirds of voters under a county charter revision adopted in 1993 known as “Save Our Parks.”

If it is approved at the Nov. 6 polls, the project would require support from the special committee Matheson sits on, and it would need to meet terms set by the Matheson family, which sued the county when it planned to build the tennis stadium. The two sides eventually reached a settlement that gave the family a say by creating the committee to approve future changes.

Matheson’s ad suggested voters shouldn’t be asked to weigh in on any changes to the park unless they are offered specific plans, rather than the more conceptual ones put forth by the tournament.

“The county is doing this backwards,” Matheson said. “The county commission should present to the public a firm plan that the public could look at and examine.”

On the contrary, Stearns said. If voters set the “outer limit” of what could be built, the county can later negotiate more favorable terms, including a shorter lease or requiring more money from the tournament.

“You can’t have a deal that involves facilities bigger or larger or grander” than what’s in the outlined plans, Stearns said.

Tournament organizers received the backing of Key Biscayne Village Council members, but only after the board stipulated certain conditions, including that the improved tennis center not be used to hold more tournaments or other events, such as concerts. The park is open to the public year-round except for the two weeks to play plus the time to set up and clear out.

“Our community probably, on balance, supports the Sony,” said Key Biscayne Mayor Frank Caplan, who is on the ballot measure’s steering committee. “We’ve become accustomed to the traffic impacts during the tournament itself, but it’s burdensome, and we don’t want those type of impacts to metastasize during the rest of the year.”

Caplan is working on getting the village, the tournament and the county, through district Commissioner Xavier Suarez, to agree to the stipulations in a written memorandum before Election Day.

Mayor Gimenez, for his part, told The Herald that he plans to vote for the measure. On Tuesday, his office issued a news release “encouraging” voters to vote on the measure, buried in a long ballot.

“It’s a county facility that needs to be upgraded, and any time that a private entity comes forward and says they will do it without using county funds, I think that’s a good thing,” he said, acknowledging that “devils are always in the details.”

“We’re not going to be putting forward anything that puts the county general fund in jeopardy,” he said.